Active - RC biquads have played, and continue to play an important role in the realization of precision voice frequency filters. Because there are as many different filters as there are uses for them, it was found to be desirable to devise a universal "building block" from which specific filter configurations could readily be derived. This development resulted in the so-called "STAR" filter. (See, for example, "STAR: A Universal Active Filter" by J. J. Friend and W. Worobey, published in the September, 1979, Bell Laboratories Record, pp. 232-236.)
More recently, a new class of active filters, using switched-capacitors, has been developed which can provide much higher order filtering on a single MOS chip. To be commercially competitive, however, a universal filter topology, comparable to the generalized STAR filter configuration is most advantageous.